The invention relates to an internal combustion engine with at least two working pistons reciprocating each in one cylinder and acting on a crankshaft through one connecting rod each and with at least one balance piston movably mounted in a balance cylinder for balancing the inertial forces, said balance piston being driven by the crankshaft through a balance connecting rod and the crank of the balance piston being disposed between the cranks of the two working pistons.
JP 62-052236 A discloses an internal combustion engine of the type mentioned herein above. The internal combustion engine is provided with two cylinders connected in series. The balance piston is disposed in the region of one cylinder of a working piston and the crankshaft is carried on three bearings. No crankshaft bearing is provided between the connecting rod of the working piston and the adjacent balance connecting rod of the balance piston. Although inertial forces are balanced by the one-sided arrangement of the balance piston, a resultant tilting moment is created normal to the crankshaft. As the working cylinders are connected in series and a driver gear for driving camshafts lying on the top is disposed between the two working cylinders, the construction is relatively bulky which is particularly problematic when used in motorcycles.
Similar internal combustion engines with at least two cylinders connected in series and one balance piston also form the subject of the publications DE 31 20 190 A, U.S. Pat. No. 5,927,242 A, U.S. Pat. No. 5,189,993 A, U.S. Pat. No. 4,940,026 A and DE 44 43 707 A.
With an internal combustion engine of the type mentioned herein above, it is the object of the present invention to achieve, in the most space saving and simplest manner possible, a balance of the inertial forces of the first and second order of magnitude.
This is achieved in accordance with the invention in that the cylinders of the working pistons are disposed in a xe2x80x9cVxe2x80x9d arrangement and that the cylinder""s axes of the cylinders of the working pistons are positioned at an angle of 0xc2x0 less than xcex1 less than 45xc2x0 to one another, the axis of the balance cylinder being arranged in a first center plane including the crankshaft axis between the two cylinders of the working pistons and wherein the following applies:             ∑              i        =        1            n        ⁢          xe2x80x83        ⁢                  r        Ai            ·              m        Ai              =                    ∑                  j          =          1                z            ⁢              xe2x80x83            ⁢                                    r            j                    ·                      m            j                          ⁢                  xe2x80x83                ⁢        and        ⁢                  xe2x80x83                ⁢                              r            A                                l            A                                =          r      l      
rA being the radius of the crank of the balance piston, r the radius of the crank of the working piston, mA the mass of the balance piston, m the mass of the working piston, lA the length of the balance connecting rod, l the length of the connecting rod of the working piston, n the number of balance pistons and z the number of working pistons. A complete balance of the inertial forces of the first and second order of magnitude is thus achieved. The xe2x80x9cVxe2x80x9d arrangement of the axes of the two working cylinders allows for a very tight arrangement of the cylinders so that space may be saved. A slight inclination of the axes of the cylinders toward each other will do. The axes of the cylinders of the working pistons should thereby preferably be positioned at an angle from 10xc2x0 to 30xc2x0, preferably of approximately 18xc2x0. In order to keep tilting moments oriented normal to the axis of the crankshaft as low as possible, it is particularly advantageous to have the axis of the balance cylinder arranged in a second center plane oriented normal to the axis of the crankshaft between two working pistons.
When the mass of the crankshaft is low, a particularly slight deflection of the crankshaft may be achieved by arranging one respective crankshaft bearing on either side and directly after the crank of the balance piston. Thus, one respective crankshaft bearing is provided between the connecting rod of each working piston and the connecting rod of the balance piston.
In accordance with the invention, the balance piston may also be configured as a pumping or a suction piston. In this way, the balance piston is capable of performing an additional function, which permits to save additional sets. It is particularly advantageous when balance piston and balance cylinder form a suction pump for evacuating the crankcase. The balance piston may thus be utilized to evacuate the crankcase during a dry sump lubrication for example. In another variant of the invention, the balance piston and the balance cylinder may form a pressure generating device for compressing the inside of the crankcase. As a result thereof, the balance piston may also be utilized to pre-compress the mixture.
In order to achieve regular ignition intervals between the two working cylinders a particular advantage is obtained when the throw of the cranks of the working pistons corresponds to the angle xcex1 of the cylinders"" axes.
In a further realization of the invention there may be provided that at least two gas exchange valves of different cylinders are actuatable through a common camshaft. Preferably, the common camshaft is thereby configured in two parts and even more preferably the two camshaft parts are joined together by an Oldham coupling in the region of the second center plane.